The present invention relates to mixtures of ceramic and metal materials.
Sintered refractory oxides and carbides have many desirable properties such as corrosion resistance, wear resistance, and mechanical strength at elevated temperatures. These materials, however, lack the thermal and mechanical shock resistance of many metals. Much research has been directed toward combining the good wear qualities of ceramic materials (i.e., refractory oxides and carbides) with the good thermal and mechanical shock characteristics of metals. Thus, the combination of a ceramic material with a metal to form a composite structure has been referred to in such terms as cermet, ceramet, ceramal, and metamic. Specific examples of these composites include the bound hard metal carbides or cemented carbides, such as, composites of tungsten carbide and cobalt. Much of the modern, high-speed machining of metals has been made possible by use of these materials. Ceramic-metal composites also find use in many other applications such as rock and coal drilling equipment, dies, wear surfaces, and other applications where wear and corrosion resistance are important.
The historical development of cemented carbide materials is described by Schwarzkopt, P. et al. in Cemented Carbides, pp. 1-13, The Macmillan Co., N.Y. (1960). As indicated, many of the carbide compositions developed, including mixed carbide systems, utilized cobalt as the binder material. These composites, including tungsten carbide bonded with cobalt, are presently widely used because of their hardness, strength, and toughness at elevated temperatures. Unfortunately, the use of ceramic materials, such as tungsten carbide, is limited by the elevated temperature strength of the cobalt binder material. Further, cobalt is a strategic material for which it is desirable to find a substitute. Materials prepared using Ni.sub.3 Al will be less expensive than materials prepared using cobalt.
U.S. Pat. No. 3,551,991 discloses preparing cemented carbides by sintering a pressed mixture of a refractory metal carbide and an iron group (Fe, Co, Ni) binder, then removing the binder, such as by exposure to boiling 20 percent HCl for seven days in the case of removing cobalt from WC/Co. The remaining skeletal structure is freed of residual acid, and is then infiltrated with a second binder, such as copper, silver, gold or alloys of nickel or cobalt with various metals, such as aluminum, niobium, tantalum, chromium, molybdenum or tungsten.
Viswanadham, R. K. et al., in Science of Hard Materials, Plenum Press, N.Y., pp. 873-889 (1983) disclose the preparation of certain WC-(Ni, Al) cermets. At page 882 it is disclosed that WC/Co composites generally are harder than composites of WC/(Ni, Al).